I. Field
This invention generally relates to the field of ophthalmic surgery, and more particularly to particular cutting techniques and methods used during ophthalmic laser surgery, including cataract and refractive surgeries.
II. Background
Vision impairments such as myopia (i.e. near-sightedness), hyperopia (i.e. far-sightedness), and astigmatism can be corrected using eyeglasses or contact lenses. Alternatively, ophthalmic surgery can be used to address these same problems. Eye surgery is also commonly used to treat conditions such as cataracts, which, if left untreated, may cause blurred vision and/or blindness.
Laser surgery is becoming a preferred technique for ophthalmic procedures as a laser is generally more precise and accurate when compared to manual surgical tools. In laser refractive surgery, such as the commonly known LASIK (Laser Assisted in Situ Keratomileusis) procedure, a surgeon uses a laser to reshape the cornea. The LASIK procedure has three steps, namely: (1) preparation of a corneal flap; (2) ablation of the corneal stroma with an excimer laser; and (3) repositioning the flap.
Previously, a microkeratome was used for corneal flap cutting and preparation, but these days, it is more common to use a non-ultraviolet (UV) laser that emits radiation with ultra-short pulse durations in the femtosecond or picosecond range. Besides cutting conical flaps, pulsed lasers are also useful for making incisions in the conical stroma to correct astigmatism. Ophthalmic lasers provide improvements over microkeratomes as more patients achieve an improved level of post-operative visual acuity in the months after surgery. Further, laser surgery tends to lessen the chance of irregular, imprecise, and inaccurate cuts and related complications.
Non-ultraviolet, ultra-short pulsed lasers are also being used for cataract surgery, including capsulotomy procedures. During cataract surgery, a pulsed laser beam may be used to create an initial incision in the cornea, to create openings in the anterior or posterior capsular bag for capsulotomy, as well as to crack or break-up the clouded cataractic lens. For example, a pulsed laser beam can be used to create an opening in the anterior capsule for an anterior capsulotomy procedure to allow access to the cataractic lens. Sometimes, a posterior capsulotomy procedure is required after cataract surgery when the posterior capsule becomes cloudy and causes vision problems. In posterior capsulotomy, the pulsed laser can be used to create an opening in a clouded posterior capsule, thereby allowing light to pass freely through the opening. In both types of capsulotomies, pulsed laser systems reduce the possibility of irregular, inaccurate, and imprecise incisions and related complications that may occur with manual surgical techniques.
Laser eye surgeries are generally performed while the patient is awake. Because a patient's eye movement can reduce the procedure's accuracy and precision, the laser system needs to compensate for and/or reduce or stabilize eye movement. One approach to do so uses an eye stabilizing device, such as a patient interface that physically attaches to the patient's eye and prevents movement. Typically, the patient interface is attached to the eye using mechanical pressure, such as vacuum suction, which can be uncomfortable for the patient, and may even cause post-operative pain and scarring. Thus, certain alternate devices have been proposed to compensate for eye movement. These include an eye tracker, which tracks the position of the eye during surgery, and provides the system with real time signals about eye position. The laser system then uses the position information from the eye tracker to adjust or reposition the laser beam before making an incision. To ensure accuracy and precision, the trajectory of the laser beam's focus must be corrected in real time to compensate for eye movement monitored by the eye tracker. But, there are delays inherent to eye trackers and their interactions with the laser system. Because the eye tracker and the laser beam delivery mechanics tend to introduce positional errors due to latency between eye movement and laser adjustment, the resulting incision pattern in the eye may deviate from that which is programmed or desired. These can result in less than ideal incisions.
Therefore, it would be beneficial to provide a pulsed laser surgical system that uses an eye tracker and allows the laser beam to make robust and accurate incisions despite eye tracker/laser beam adjustment latency issues.